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<p class="header"><a class="header" href="intro.htm">Orbiter</a> &gt; <a class="header" href="mainmenu.htm">Main menu</a> &gt; <a class="header" href="options.htm">Options</a> &gt; <a class="header" href="vishelper.htm">Visual helpers</a> &gt; Force vectors</p>

<h1>Force vectors</h1>

<p>Orbiter can provide a graphical display of the force vectors currently acting on a spacecraft. This option is particularly useful for educational applications, to provide a direct feedback of the effects of environmental parameters (gravity, atmosphere) and user input (e.g. change of lift as a function of changing angle of attack).</p>

<p>The display of force vectors can be activated and configured via the <i>Force</i> tab in the Visual helpers dialog (<kbd class="ctrl">Ctrl</kbd> <kbd class="ctrl">F9</kbd>).</p>

<p>Tick <i>Body force vectors</i> to enable the vector display.</p>

<p>Orbiter allows to show a number of separate linear force components as well as the resulting total force:</p>

<p><table col=3>
<tr><td>Weight</td><td>G (yellow)</td><td>force due to gravitational field</td></tr>
<tr><td>Thrust</td><td>T (blue)</td><td>force generated by the vessel's propulsion system</td></tr>
<tr><td>Lift</td><td>L (green)</td><td>lift force generated by lifting airfoils in airflow</td></tr>
<tr><td>Drag</td><td>D (red)</td><td>drag force generated by motion through atmosphere</td></tr>
<tr><td>Total</td><td>F (white)</td><td>total force acting on the vessel</td></tr>
</table></p>

<p>Note that the total force shown may not be equal to the sum of the four component forces, because additional forces may be acting on the vessel (e.g. user-defined forces).</p>

<p>Linear forces are shown graphically as vector arrows originating at the vessel's centre of gravity. The vector lengths are proportional to the force magnitudes, or logarithm of the magnitudes, depending on the <i>Scale</i> setting. The lengths can be adjusted with the provided slider. In addition, the magnitudes are also shown numerically in units of Newton [N].</p>

<p>In addition to the linear forces, Orbiter can also display the acting total torque,</p>

<p align="center">
<b>M</b> = &Sigma;<sub>i</sub> <b>M</b><sub>i</sub> = &Sigma;<sub>i</sub> <b>F</b><sub>i</sub> x <b>r</b><sub>i</sub></p>

<p>The torque vector is shown w.r.t. the centre of gravity of the vessel. The numerical value is shown in units of Newton x metre [Nm].</p>

<p>Note that for forces that are not generated at the vessel's centre of gravity (e.g. the lift vector), the total force displayed is broken up into a linear component originating at the centre of gravity, and a corresponding torque.</p>

<p>The opacity of the displayed force vectors can be adjusted with the <i>Opacity</i> slider, from completely transparent to completely opaque.</p>
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